Diesel fuel containing di-tertiary alkyl sulfides as ignition promoters



Patented Oct. 21, 1952 DIESEL FUEL CONTAINING I DI-TERTIARY ALKYL SULFIDES AS IGNITION PRO- MOTERS Lawrence T. Eby, Roselle, N. J a'sslgnor to Standard Oil Development Company, a corporation of Delaware No Drawing. Application June 4, 1946,

Serial No. 674,373

3 Claims.

1 This invention relates to a new type of additive for improving the properties of hydrocarbon olls, particularly lubricatin oils and diesel fuels.

The new additive of the present invention is a dialkyl sulfide having tertiary alkyl radicals of at least 8, and most suitably from 8 to 25, carbon atoms in each alkyl group, such alkyl groups being connected by at least 2, and preferably from 2 to 4, sulfur atoms. The new type of additive, when dissolved in a mineral lubricating oil, imparts to such oil the property of resisting corrosion of metal surfaces, particularly the copperlead and cadmium-silver alloy bearings now commonly employed in automotive engines. Such oil also has the property of resisting deterioration by oxidation, and it resists sludge formation, thus providing for a cleaner engine condition. The

form in which the sulfur of the additive is held in chemical combination makes it possible to introduce an unusually large proportion of sulfur into the oil without at the same time causing the oil to stain copper, bronze and other metal surfaces with which it comes into contact. In these respects many of the compounds of the present invention have been found to be superior to the aliphatic mercaptans described in my U. S. Patent 2,382,700. I

In somewhat larger quantities the additives of the present invention impart load carrying properties to the oil, enabling the same to be used as an extreme pressure lubricant. When the dialkyl sulfides contain large amounts of sulfur, as in the hexasulfides and octasulfides, they may be conveniently employed in cutting'oils and the like.

The compounds herein disclosed are likewise useful as diesel dopes, for increasin the cetane number of diesel fuels.

The tertiary alkyl'polysulfides of the present invention are generally employed in unsubstituted form, but they are likewise useful for the purposes indicated when one or more of the hydrogen atoms of the alkyl groups is replaced by substituents, such as carboxyl, hydroxyl, alkoxy, nitro, keto, amino, aldehydo, cyano, cyanate, thiocyanate, isothiocyanate, amido, sulfo, sulfate, thiophosphate, p-hosphona-te, sulfonate or ester groups, metal substituted carboxyl and hydroxyl groups, halogen atoms, and the like.

The di-tertiary-alkyl disulfides are most conveniently prepared by the oxidation of a tertiary mercaptan, for example, with oxygen, a halogen, or sulfur. The tertiary mercaptans may conveniently be prepared by reacting a tertiary olefin with hydrogen sulfide in the presence of a Friedel-Crafts type catalyst, as described more particularly in the co-pending application of .Mikeska and Eby, Serial Number 512,776, filed- December 3, 1943, now abandoned. The tertiary alkyl disulfides are most readily prepared by the above methods. The trisulfides may be prepared by reacting the tertiary mercaptan with sulfur or with sulfur dichloride, or byreacting the disulfide with sulfur. Similarly, tetrasulfldes may be prepared by reacting the tertiary mercaptan with sulfur monochloride or with sulfur, or by reacting the trisulfide with sulfur. Still higher sulfides may be prepared by using larger quantitles of the sulfur halides in the reaction 'with the mercaptan or by reacting the lower sulfides with additional sulfur. All of the above-described reactions may take place without a solvent, or by the use of a suitable solvent, such as chloroform. Loosely combined sulfur in the products may be removed by means of a sweetening or sulfur dissolving agent, 'e. g., an ammonium sulfide solution. Numerous examples will be given below in which methods for the preparation of these compounds will be described in detail.

Example 1.Di-tert.-octyl trisulfide 46 g. (1 mol.) of tert.-octyl mercaptan (pre- :d by reacting diisobutylene with H28) and 200 cc. of chloroform were placed in a glass flask with stirrer, return condenser and dropping funnel. 51.5 g. (0.5 mol) of SClz was added dropwise at 25-45 C. The mixture was heated under reflux for two hours, after which the solvent was stripped off by distillation, and all volatile constituents were removed at 2 mm. pressure over a boiling water bath. The clear light yellow liquid residue weighed 152.4 g. and contained (by Parr bomb analysis) 30.42% S and 0.20% Cl, corresponding to the formula C8H1'I-S3.1-C8H17- Example 2.--.S'weetened di-tert.-octyl trisulfide The procedure of Example 1 was repeated, but after refluxing the chloroform solution was sweetened by stirring twice with an ammonium sulfide solution prepared from 150 cc. of concentrated ammonium hydroxide and 10 g. of Has. The chloroform layer was washed with water. dried over anhydrous KzCOa, and stripped of solvent and volatile constituents at C. and 2 mm. pressure. The light yellow liquid residue weighed 138.5 g. and contained 30.68% S and 0.26% 01, corresponding to the formula CsH17Ss.1CsH17 Example 3.-Di-tert.-octyl tetrasulfide 146 g. (1 mol) of tert.-octyl mercaptan and 200 cc. of chloroform were placed in a glass flask with stirrer, return condenser and dropping funnel. 67.5 g. (0.5 mol) of SaCl: was added dropwise at 25-41 C. The mixture was then heated under reflux for 2 hours. The solvent was stripped off by distillation, finally removing all volatile constituents at 2 mm. pressure over a boiling water bath. The clear yellow liquid residue weighed 168.1 g. and contained 36.15% S and 0.85% 01, corresponding to the formula CaI-I1'1-S4-CaHrz Example 4.Sweetened di-tert.-octyl tetrasulflde The procedure of Example 3 was repeated, but after refluxing the chloroform solution was sweetened by stirring twice with an ammonium sulfide solution, as in Example 2. The chloroform solution was washed with water, dried over anhydrous X2002. and stripped of solvent and volatile constituents at 100 cc. and 2 mm. pressure. The light yellow liquid residue weighed 154.9 g. and contained 34.45% S and 0.67% Cl, corresponding to the formula CaH1'1S3.e-CaI-Ii7.

Example 5.-Sweetened di-tert.-octyl tetrasulflde The procedure of Example 4 was repeated to give a product containing 34.23% S and 0.78% Cl, corresponding to the formula CaHm-Szm-CaHn.

Example 6.Di-tert.-dodecyl trisulfide 202 g. (1 mol) oi tert.-dodecyl mercaptan (prepared by reacting triisobutylene with H28) and 51.3 g. (0.5 mol) of SCla were reacted in the presence of 200 cc. of chloroform according to the procedure of Example 1. The liquid residue contained 23.51% S and 0.65% C1, corresponding to the formula C12H2sS3.a--C12H25.

Example 7.-Sweetened df-tert.-dodecyl trisulfide Sweetening" of the product of Example 6 by treatment with ammonium sulfide solution as in Example 2 gave a product containing 23.83% s and 0.46% Cl, corresponding to C12H2s-Sa.:-C12H2s Example 8.Di-tert.-dodecyl tetrasulfide 202 g. (1 mol) of tert.-dodecyl mercaptan and 67.5 g. (0.5 mol) of SaCh were reacted in the presence of 200 cc. of chloroform solvent according to the procedure of Example 3. The liquid residue contained 29.90% S and 0.32% Cl, corresponding to the formula CnHw-Su-Cnflza.

Example 9.-Sweetened di-tert-dodecul tetrasulfide Sweeteningf of the product of Example 8 by treatment with ammonium sulfide solution as described in Example 4 gave a product containing 28.60% S and 0.35% Cl, corresponding to the formula CisHst-Sis-CMHM.

Example 10.Di-tert.-octyl trisulflde 257.5 g. (2.5 mols) of S012 was dropped over a period of minutes into 730 g. (5 mols) of tert.- octyl mercaptan while stirring. The temperature rose to C. during the addition and was kept at 75 C. for one hour and 37 minutes thereafter while air was blown through the mixture to remove HCl. After cooling, the mixture was stirred with a solution of ammonium sulfide made from 750 cc. of concentrated ammonium hydroxide of 40 g. of Has. The organic layer was extracted with petroleum ether, washed three times with water and dried over anhydrous KzCOs. The solvent was stripped oil by distillation at 100 C. and 1 mm. pressure. The yellow liquid product weighed 641 g. and was slightly hazy. This haziness was removed by filtering through diatomaceous earth. Analysis showed 29.16% S and 0.41% C1.

The following tables show by comparison the extent to which the sulfur atoms in the polysulflde products are held in the molecule-in the tertiary alkyl compounds,. as compared to similar compounds prepared from primary mercaptans. The primary mercaptan employed in preparing the polysulfides was Lorol-mercaptan, which is a mixture of mercaptans of 10 to 16 carbon atoms per molecule, derived from a product obtained in the catalytic hydrogenation of cocoanut oil acids. It will be seen that, regardless of the number of sulfur atoms introduced into the original polysulfide product obtained from the Lorol mercaptan, the sweetening process reduced the number of sulfur atoms to approximately 3. On the other hand, upwards of 4 atoms of sulfur were retained in the product, derived from tert-.dodecyl mercaptan.

POLYBULFIDES FROM TERTIARY DODECYL MERCAPTAN Unsweetened Polysulflde Sweetened Polysulflde Moi Ratio of g MI I e Number of We! Number of lyses Hand? Sulfur Atoms Suliur Atoms per Molecule Percent Percent per Molecule Percen'. Percent 5 01 S 01 POLYSULFIDES FROM "LOROL" MEROAPTAN Unsweetened Polysulfide Sweetened Polysulflde Mol Ratio of Sulfur Halide Mercaptan to Number of Analyses Number of Analyses Hand Sulfur Atoms Sulfur Atoms per Molecule Percent Percent per Molecule Percent Percent 7 .Example 11.-Bcarinc corrosion tests Blends of various-tertiary-alkyl polysulfldes of the present invention in a lubricating 011 base were submitted to a corrosion test designed to measure the effectiveness of the products in inhibiting the corrosiveness of a typical mineral lubricating oil toward the surface of copperlead bearings. For a comparison, blends of certain tertiary alkyl mercaptans were similarly tested, The base oil employed was a well refined solvent extracted paraiilnic type mineral lubricating oil of SAE viscosity grade, and each blend contained 1% of additive. The test was conducted as follows: 500 cc. of the oil was placed in a glass oxidation tube ('13 inches long and 2% inches in diameter) fitted at the bottom with a V inch air inlet tube perforated to facilitate air distribution. The oxidation tube was then immersed in a heating bath so that the oil temperature was maintained at 325 C. during the test. Two quarter sections of automotive bear -.ings of copper-lead alloy of known weight having a total area of sq. cm. were attached to opposite sides of a stainless steel rod which was then immersed in the test oil and rotated at 600 R. P. M., thus providing sufficient agitation of the sample during the test. Air was then blown through the oil at the rate of 2 cu. ft. per hour. At the end of each 4-hour period the bearings were removed, washed with naphtha and weighed to determine the amount of loss by corrosion.

The bearings were then repolished (to increase the severity of the test), reweighed, and then subjected to the test for additional 4-hour periods in like manner. The results are given in the following table as corrosion life, which indicates the number of hours required for the bearings to lose 100 mg. in weight, determined by interpolationof the data obtained in the various periods.

Bearing Additive Qorrosion Life (Hrs) No 6 Tert octvl mercaptan 14 Ten -dodecv] mercaptan 16 D1 Lorol disn e... 11 Di-tert.-octvl disulfide 40 Di tert. dodecvl disulfide 40 Di-tertwoctyl trisuliide (product oi' Ex. 2). 4s Di-tert.-octvl tetrasulfide (product of Ex. 5) 48 Di-tert.-dodecvl trisulfide (product of Ex. 6) 23 Di-tert. dodccyl trisulfide (product of Ex. 7) 1 32 Di-ieit.-dodec l tetrasulfide (product of Ex. 9) 1 50 Di-tert.-dodecyl hexasulflde 1 50 Di-tert.-dodecyl octasuliide 1 57 None 10 Di-n-tut 'l disulfide 2 Di-n-amyl disulfide l1 1 Blackens copper strip at 212 Ffafter 3 hours. I Blackens copper strip at 212 F. after 6 hour. All other blends did not blacken copper strip in 3 hours.

The above data indicate that the tertiary alkyl polysuliides are distinctly superior to the corresponding mercaptans and to the primary dialkyl disulfide as corrosion inhibiting agents. It-

is further shown in the table that a number of unsweetened products showed a tendency to stain metallic surfaces, illustrated by the copper strip test, while other products, chiefly sweetened products, were free from this tendency. This shows Example 12.--Bearina corrosion tests with detergent Blends containing 1% each of examples of tertiary alkyl tetrasulfldes, both with and without the further addition of calcium suifonate, were tested by the method described in Example 11, using as a base stock the same lubricating oil. Similar tests were made with a commercial corrosion inhibitor, sold under the trade name Paranox 12." The results are as follows:

Bearing Corrosion Lilo Additive out g g 1% a e um a clum Dlilc Sulfonatc Sulionatc mu None 6 Paranox l2" 45 22 2% Di-tert.-octyl tetrasulflde. 46 42 4 Di-tert.-dodecyl tetrasulflda. 39 32 1 Example 13.--Chevr0let engine test In this test a base oil was used which consisted of a solvent extracted Mid-Continent parafllnic oil of 46 seconds Saybolt viscosity at 210 F. and V. I., to which had been added suflicient polybutene V. I. improver to give a lubricating oil of V. I. and 52 seconds viscosity at 210 F. An unblended sample of this base oil and a sample of the 011 containing 1% of di-tert.-octyl trisulfide, prepared as described in Example 10, were tested in a Chevrolet engine run for 36 hour periods under the following conditions: 14.2/1 air/fuel ratio, 30 brake horse power, 3150 R. P. M., 280' F. oil temperature, 200 F. water jacket temperature. After .each engine test was completed the engine parts were examined and given demerit ratings based on their condition, particular attention being paid to the ring zone conditions. The individual ratings were weighted according to their relative importance and an overall demerit rating calculated from them. It should be pointed out that the lower the demerit rating the better the engine condition, and hence the better the performance of the oil. The results obtained are presented in the table below:

It will be seen that the additive produced a marked improvement in the engine condition.

The additives of the present invention have i also been found to be highly effective as extreme pressure agents, 1. e., agents for increasing the load carrying capacity of a lubricating oil. This property is illustrated in the following example.

7 V Example 14.-Tests of load carrying P perties To determine the load carrying properties ofoils containing various examples of the additives of the present invention, blends were prepared containing of various compounds in a gear 011 consisting of a mixture of a steam refined Pennsylvania cylinder oil and a light paraillnic Mid-Continent distillate oil, and such blends were tested in the standard SAE Test Machine, which was operated at 1000 R. P. M. and 14.6/1 slip ratio. The results are as follows:

S. A. E. Machine Additive Scale Rating None Di-n-amyl disulilde 170 Di-Loro1" disulflde 110 Di-LoroY' trisuliide 180 Di-tert.-octyl disulilde. 320 Di-tert.-dodecyl disulfide. 195 Di-tert.-octvltrisu1flde 450 DE-tert-dodecyl trisulfide 450 Di-tert.-octyl tetrasulflde 450 Di-tert.-dodecy1 tetrasulfide 490 Di-tert.-dodecyl hexasulfide 4o0 Di-tert.-dodecyl octasulflde 1 450 1 These oil blends were found to blacken a copper strip when contacted (or one hour at 212 F., while all other blends fail to blacken the copper strip. It is obvious from the above data that the tertiary alkyl polysulfldes are distinctly superior to the primary alkyl disulfides as extreme pressure agents.

The additives of the present invention when employed in mineral lubricating oils as corrosion inhibitors are advantageously used in proportions of from 0.1 to 2.0%, and when employed as extreme pressure agents the proportion will be advantageously from 2 to 10% or higher.

Although the tertiary alkyl polysulfides of the present invention may be employed as the sole additives in lubricating compositions, their use in conjunction with other materials, particularly with detergent type additives, will often be found advantageous. It is thus contemplated to use these compounds in lubricating compositions containing such other addition agents as metal phenates, metal alkyl phenol sulfides, metal organo-phosphates, thiophosphates, phosphites and thiophosphites, metal alcoholates and ketonates, metal sulfonates, metal carboxylates, metal phosphonates, metal xanthates and thioxanthates, metal thiocarbamates, and the like.

Thus, the addition agents of the present invention may be used in mineral lubricating oils containing one or more of the following representative materials: I

Barium tert.-octyl phenol sulfide Calcium mahogany sulfonates Calcium dichlorostearate Nickel amyl xanthate Aluminum naphthenate Zinc methyl cyclohexyl dithiophosphate Tin salt of wax alkylated phenol sulfide Barium octadecylate Magnesium cetyl phenate Barium diamyl phenol sulfide Zinc diisopropyl salicylate Calcium cetyl phosphate The lubricating oil base stocks employed in the blended lubricating oils of this invention may be straight mineral lubricating oils, or distillates derived from parafilnic, naphthenic, asphaltic or mixed base crudes, or, if desired, various blended oils may be employed as well as residuals, particularly those from which asphaltic constituentshave been carefully removed. The oils may be refined by conventional methods using acid. alkali and/or clay or other agents such as aluminum chloride, or they may be extracted oils produced, for example, by solvent extraction with solvents of the ype of phenol, sulfur dioxide, furfural, dichloroethyl' ether, propane, nitrobenzene, crotonaldehyde, etc. Hydrogenated oils or white oils may be employed as well as synthetic oils prepared, for example. by the polymerization of oleflns or by the reaction of oxides of carbon with hydrogen or by the hydrogenation of coal or its products. In certain instances cracking coil tar functions and coal tar or shale oil distillates may also be used. Also, for special applications, animal. vegetable or fish oils or their hydrogenated or voltolized products may be employed, either alone or in admixture with mineral oils.

For the best results the base stock chosen should normally be that oil which without the new additive present gives the optimum performance in the service contemplated. However, since one advantage of the additives is that their use also makes feasible the employment of less satisfactory mineral oils or other oils, no strict rule can be laid down for the choice of the base stock. Certain essentials must of course be observed. The oil must possess the viscosity and volatility characteristics known to be required for the service contemplated. The oil must be a satisfactory solvent for the additive, although in some cases auxiliary solvent agents may be used. The lubricating oils, however they may have been produced, may vary considerably in viscosity and other properties depending upon the particular use for which they are desired, but they usually range from about 40 to 150 seconds Saybolt viscosity at 210 F. For the lubrication of certain low and medium speed diesel engines the general practice has often been to use a lubricating oil base stock prepared from naphthenic or aromatic crudes and having a Saybolt viscosity at 210 F. of 45 to 90 seconds and a viscosity index of 0 to 50. However, in certain types of diesel service, particularly with high speed diesel engines, and in gasoline engine service, oils of higher viscosity index are often required, for example up to 75 or 100, even higher, viscosity index.

In addition to the materials to be added socording to the present invention, other agents may also be used such as dyes, pour depressors, heat thickened fatty oils, sulfurized fatty oils,

organo-metallic compounds, metallic or other octyl alcohol, CsI-InOH, lauryl alcohol, CmHzsOH,

cetyl alcohol, CmHasOH, stearyl alcohol, sometimes referred to as octadecyl alcohol, CnHs-IOH,

and the like; the corresponding oleiinic alcohols such as oleyl alcohol; cyclic alcohols, such as naphthenic alcohols; and aryl substituted alkyl L 9 alcohols,'for instance, phenyl octylalcohol, or. octadecyl benzyl alcohol, or mixtures of these various alcohols, which may be pure or substantially pure synthetic alcohols. One may also use mixed naturally occurring alcohols such as those found in wool fat (which is known to contain a substantial percentage of alcohols having about 16 to 18 carbon atoms) and in sperm oil (which contains a high percentage of cetyl alcohol); and although it is preferable to isolate the alcohols from those materials, for some purposes the wool fat, sperm oil or other natural products rich in alcohols may be used per se. Products prepared synthetically by chemical processes may also be used, such as alcohols prepared by the oxidation of petroleum hydrocarbons, e. g., paraflin wax, petrolatum. etc.

In addition to being employed in crankcase lubricants and in extreme pressure lubricants; the additives of the present invention may also be used in industrial lubricants, process oils, engine flushing oils, turbine oils, insulating and transformer oils, steam cylinder oils, slushins' and rust preventing compositions and greases. Also their use in motor fuels, diesel fuels and kerosene is contemplated. The particular effectiveness of the additives as ignition promoters in diesel fuels is illustrated by tests of cetane number improvement resulting from the additionof the additives under discussion. The conditions of the tests are described in the following example, wherein itis shown that the cetane number of the fuel is markedly increased by adding compounds of the present invention. The higher polysulfides are more eifective than the lower polysulfides, the tetrasuliides being particularly effective. The primary dialkyl tetrasulfldes heretofore known in the art have been too corrosive to copper to be useful as an additive for the fuel. The tertiary dialkyl tetrasulfldes of this invention. especially after being sweetened, have an excellent capacity for raising the cetane number of the diesel fuel, the resulting fuel being non-corrosive to copper and having excellent storage stability.

Example 15.-Diesel fuel tests Cetane number determinations were made with an unblended high speed diesel fuel of 50 cetane-number, consisting of a major proportion of virgin gas oils with not more than 25% of cracked gas oil, and with this base fuel containing 1% of various additives of the present invention. The results are as follows:

Octane Additive 9:28: Number Increase None 50 Tert.-octyi mercaptam 61 1 Di-terL-octyl disulfide. 5 Di-tert.-octyl trisuliidc 67 7 Di-tert.-oetyl tetrasulilde 10 All of the above fuels were found to pass the three hourcopper strip corrosion test at 212 F.

In addition to the uses described above, the compounds of the present invention are likewise useful as plasticizers in rubbers, as sulfur carrying compounds (vulcanizing agents) for rubber and similar products, and as stabilizing agents for hydrocarbon polymers.

The present invention is not to be considered as limited by any of the examples described herein, which are given by way of illustration only REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,374,983 De simo May 1, 1945 2,415,852 Schulze et al Feb. 18, 1947 2,526,041 Olin Oct. 17, 1950 

1. A HYDROCARBON DIESEL FUEL CONTAINING AN IGNITION-PROMOTING AMOUNT OF A DIALKYL SULFIDE HAVING TERTIARY ALKALI RADICALS OF FROM 8 TO 25 CARBON ATOMS AND HAVING 4-8 SULFUR ATOMS LINKING THE RESPECTIVE TERTIARY ALKYL RADICALS. 